The present invention relates to an inkjet printer that ejects ink on a recording medium to print an image thereon.
There has been known a so-called serial type inkjet printer. In the serial type inkjet printer, an inkjet head is mounted on a carriage that reciprocates in a direction perpendicular to a feeding direction of a recording sheet (i.e., in a width direction of the recording sheet). A tube is connected to the ink head to supply ink from an ink supplying source. The inkjet head ejects the ink supplied from the ink supplying source to print a desired image on the recording sheet. When the image is printed, the inkjet head ejects the ink while the carriage is reciprocating.
When the carriage changes its moving directions, relatively large acceleration acts on the inkjet head. Then, a large acceleration acts on the inkjet head and the tube connecting the inkjet head with the ink supplying source. This large acceleration generates dynamic pressure in the ink within the tube. The dynamic pressure may transmit to the inkjet head and make the ink ejection unstable.
In order to overcome the problems mentioned above, an inkjet printer disclosed in Japanese Patent Application Provisional Publication No. P2002-166568 employs a sub-tank that is divided into a first ink room and a second ink room. The first ink room is supplied with ink from an ink cartridge through a tube and has an air space for accumulating the bubbles introduced into the first ink room. The second ink room is in fluid communication with an inkjet head to supply ink thereinto. The first and second ink rooms are connected with each other at upper portions thereof to allow ink to flow from the first ink room into the second ink room. A filter is provided between the first and second ink rooms to trap the bubbles in the ink.
In the above-mentioned sub-tank, the air accumulated in the air space defined above the first ink room absorbs the dynamic pressure generated in the ink by the reciprocation of the carriage, resulting in a stable ink ejection from the inkjet head and hence a good printing quality.
In the above-mentioned sub-tank, however, the surface of the ink exposed to the air accumulated in the first ink room increases as the volume of the accumulated air increases and the level of the ink comes down. The increase of the ink surface causes coagulation of the materials contained in the ink, which inhibits smooth flow of the ink.